Chloroisocyanuric acids such as trichloroisocyanuric acid ("TCCA") have long been used as sanitizers for water systems such as swimming pools, spas, etc. One drawback to this use however, is that chloroisocyanuric acids generate chlorine or chlorine-containing gases that are hazardous to human health and corrosive to water treatment equipment. Corrosive chlorine gas also adversely affects the packaging used to store the chloroisocyanuric acid, so that storage problems associated with the decomposition of the sanitizer are compounded by storage problems associated with the corrosion of the packaging itself.
The evolution of chlorine gas from TCCA-containing compositions is especially pronounced when the TCCA is wet, such as when the TCCA is formulated into solid pucks or tablets that are placed into water to sanitize the system. For example, in swimming pools it is common to use chemical feeder systems that rely on pumps to recirculate the treated water throughout the system. In many cases, the pump is turned off at night, and when the attendant opens the feeder in the morning the initial shock from built-up chlorine gas may be strong enough to make the attendant sick or disoriented. These problems are well known to the swimming pool chemical industry, and sanitizers that have a reduced level of chlorine gas evolution have long been sought.
It is also known that boron derivatives such as sodium tetraborate (borax) provide beneficial algicidal and fungicidal properties to water. Unfortunately however, boron derivatives are known to promote the undesirable chlorine gas evolution from TCCA as described above. For example, U.S. Pat. No. 5,021,186 to Ota et al. shows that compositions comprising sodium tetraborate (9 g) and TCCA (21 g) generate 6.3 mg chlorine gas, compared to the 0.31 mg gas generated by a like amount of TCCA alone.
Finally, it is known that in some situations aluminum sulfates improve the stability of chloroisocyanuric acids and correspondingly reduce the evolution of chlorine-containing gas from such compositions. The benefits of adding alum to TCCA are limited however, and are not believed to be enhanced by adding gas-generating compounds such as boron derivatives to the alum/TCCA compositions. In fact, the contrary expectation has prevailed in the art, with skilled artisans believing that adding boron derivatives to the alum/TCCA compositions would result in unsatisfactory levels of chlorine gas generation.
In spite of the known disadvantages of using chloroisocyanuric acid and borax in water treatment systems, a need continues for trichloroisocyanuric acid compositions that take advantage of the beneficial algicidal and/or fungicidal properties of borax yet are relatively safe and non-corrosive. The present invention addresses that need.